Glenoid lateralization influences active internal rotation after reverse shoulder arthroplasty

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Reconstructive Surgery

Background:

• Internal rotation (IR) improvement is inconsistent following reverse total shoulder arthroplasty (RSA).
• This study investigates glenoid-sided lateralization's impact on postoperative IR in RSA.

Purpose of the Study:

• To evaluate the relationship between postoperative internal rotation (IR) and glenoid-sided lateralization after reverse total shoulder arthroplasty (RSA).
• To assess the effect of metallic lateralization on shoulder function and patient outcomes.

Main Methods:

• A multicenter retrospective study analyzed 455 RSA cases with at least 1-year follow-up.
• Patients were grouped by glenoid lateralization (0-2 mm, 4 mm, 6 mm, 8 mm).
• Primary outcome: active IR (spinal level and degrees at 90° abduction); secondary outcomes: forward flexion, external rotation, strength, and patient-reported outcomes (PROs).

Main Results:

• Glenoid lateralization of 8 mm showed significantly improved IR compared to all other groups.
• 6 mm of lateralization also yielded significantly better IR than 0-2 mm and 4 mm groups.
• Glenoid lateralization was the sole implant variable significantly associated with improved IR; glenosphere diameter and humeral version impacted IR measured in degrees.

Conclusions:

• Glenoid lateralization of 6-8 mm is associated with improved active IR at 1 year post-RSA.
• No significant differences in forward flexion, external rotation, or PROs were noted between lateralization groups.
• Multivariable analysis indicated increased humeral retroversion correlated with increased IR, while increasing glenosphere diameter correlated with decreased IR.